Absorbent batts made from fibers such as fluffed wood pulp fibers or other cellulosic fibers are used in sanitary napkins, disposable diapers, absorbent dressings, and other articles as a medium which is highly absorbent and has considerable capacity for holding aqueous fluids. The batts are made from individualized cellulosic fibers, usually wood pulp fibers, which are used because of their highly absorbent properties and because of their softness and low cost. However, such absorbent wood pulp or other cellulosic fiber batts have rather considerable loft or bulkiness properties, which means that the article employing such batts often tends to be rather bulky. This can add to the expense of shipping and packaging such articles. Consider, for example, the bulky packages in which disposable diapers and sanitary napkins are ordinarily marketed.
It would be a desirable objective to be able to reduce the thickness and bulkiness of wood pulp or other cellulosic fiber batts without a concomitant reduction in the liquid holding capacity of such materials. The present invention is directed to such a means whereby an absorbent polymer is incorporated in a fibrous batt, such as a wood pulp batt, in a convenient form such that it can utilize a high proportion of the theoretical capacity of the absorbent polymer. By such incorporation, the bulk or loftiness of the fibrous batt can be significantly reduced. This can reduce shipping and packaging costs, and in many such articles cases can make such articles more convenient and comfortable to wear.
It has, of course, been attempted to incorporate superabsorbent polymers into absorbent bodies for some time now. However, it is not easy to employ such superabsorbent polymers in a way that utilizes a major portion of the theoretical capacity of such polymers to absorbe liquid. The problem is that when the first portion of liquid strikes the surface of a superabsorbent polymer, a gel is formed which retards the transport of liquid therethrough and slows down and even prevents the passage of liquid to the interior of the particle of polymer. Attempts to avoid this problem by employing finely divided granules of superabsorbent polymers have met with limited success because it is difficult to affix the granules in place. Therefore, it has heretofore proven difficult to combine the obvious low cost and availability of wood pulp fibers with the high liquid holding capacity of superabsorbent polymers to produce an absorbent composite having a high capacity for holding liquid, but which has reduced bulk and loftiness when compared with wood pulp batts of similar liquid holding capacity.
Most absorbent pads, such as fluffy wood pulp batts mentioned above, have heretofore been made of all, or almost all, cellulosic fibers such as wood pulp, cotton, or rayon. The reason for this is clear--cellulosic fibers have desirable absorbent properties and are relatively inexpensive. Other types of fibers, however, have properties not possessed by cellulosic fibers, which would make them desirable to use in absorbent pads if they had absorbent properties. For instance, fusible fibers made from polyethylene or polypropylene can be heat bonded, while cellulosic fibers cannot. The ability to be heat bonded can be a significant processing advantage. The present invention provides a process for producing fluffy, absorbent fibrous batts from any kind of fiber, even from fibers which intrinsically lack absorbent properties.